Highly active and selective catalysts for the production of unsaturated nitriles, methods of making and using the same

ABSTRACT

An improved catalyst for the production of unsaturated nitriles from their corresponding olefins, the catalyst having the atomic ratios described by the empirical formula Bi a  Mo b  V c  Sb d  Nb e  A f  B g  O x  and methods of using the same.

This application is a division of application Ser. No. 09/228,885, filedJan. 11, 1999, now abandoned which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to new ammoxidation catalysts for theproduction of unsaturated nitrites from their corresponding olefins.More specifically, the present invention is directed to an improvedammoxidation catalyst containing niobium as an essential element forenhancing activity and selectivity of the catalyst system and methods ofusing the same.

2. Description of Related Art

Several publications are referenced in this application. The referencesdescribe the state of the art to which this invention pertains and arehereby incorporated by reference.

It is known in the art that the bismuth-molybdenum system plays a rolein electron donor/acceptor mechanisms for selective oxidation andammoxidation. Therefore different mechanisms have been proposed based onthis property [Delmon et al. (New Development in Selective Oxidation byHeterogeneous Catalysis, Vol. 72, 1992, p. 399-413) and Encyclopedia ofChemical Technology (Kirk-Othmer, Vol. 1, 4th edition, page 358)]. Inthese mechanisms, molybdenum was shown to be responsible for oxygen andnitrogen uptake and insertion into the substrate, while bismuth playsthe role of H-abstraction of the methyl group in the β position.Therefore, bismuth and molybdenum should be present on the catalystsurface and adjacent in order to form the suitable active phase for thisreaction. It should be noted that the deficiency of bismuth on thecatalyst surface leads to the total oxidation reaction of the substrate.

It is also well known that antimony plays the role of a donor and thuscould improve the selectivity of the catalyst. Antimony can also play anadditional role of isolating the vanadium active centers which arehighly active towards the oxidation reaction. This leads to minimizingthe total oxidation reaction and directs the reaction towards thedesired product.

Many catalysts have been disclosed for the foregoing reactions. One suchcatalyst is described in U.S. Pat. No. 4,062,885, where BiMoSbV systemswere used as active elements. The catalyst was used for the preparationof phthalonitrile by the ammoxidation of ortho-xylene. The use of suchcatalysts for oxidation or ammoxidation reactions involving unsaturatedaliphatic hydrocarbons is not mentioned.

U.S. Pat. No. 4,040,978 relates to a catalyst for ammoxidation reactionscontaining bismuth molybdate mixed with other elements.

U.S. Pat. No. 4,405,498 relates to a catalyst for oxidation andammoxidation reactions containing BiMoVSb with additional elementsselected from groups IA, IIA, IVA, VA, VIA, IB, IVB and VIIB of theperiodic Table of the Elements. Elements from group VB of the periodictable are not disclosed in this patent.

U.S. Pat. No. 4,600,541 relates to a catalyst comprising FeBiMo andpromoters such as Pd, Pt, Os and Ir.

More recently, European Patent Publication No. 0 475 351 A1 relates to acatalyst containing KFeSbMo which could be promoted by Nb and W. Thebest yield was achieved with a catalyst of the formula Fe₁₀ Sb₁₀ Mo₉ Bi₂K₀.6 Ni₅.5 W₀.3 B₀.75 P₀.75 (SiO₂)₇₀.

European Patent Publication No. 0 573 713 B1 relates to a catalystcomprising MoBiFeCoNiCr promoted with at least three other promotersselected from alkali metals, alkaline earth metals, rare earth metals,Nb, Tl and As, with Fe, Co, Ni and Cr as essential catalyst components.

U.S. Pat. No. 5,688,739 relates to a multi-component catalyst. The baseof this catalyst is bismuth molybdenum. Germanium was added as anessential element. The use of niobium was not disclosed in this patent.

None of the prior art references discloses or suggests catalysts whichprovide high performance for the selective production of unsaturatednitriles from their corresponding olefins. Accordingly, it would bedesirable to produce an improved catalyst for use in the selectiveproduction of unsaturated nitrites from their corresponding olefins.

OBJECTS OF THE INVENTION

It is an object of the invention to overcome the above-identifieddeficiencies.

It is another object of the invention to provide a useful, improvedcatalyst for the production of nitrites from their correspondingolefins, particularly for the production of acrylonitrile frompropylene.

It is a further object of the invention to provide a process for theproduction of acrylonitrile at high yields by vapor phase catalyticammoxidation of propylene in a fluidized or fixed bed reactor.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description.

SUMMARY OF THE INVENTION

The present invention relates to an improved catalyst for the productionof unsaturated nitriles from their corresponding olefins, the catalysthaving the atomic ratios described by the empirical formula set forthbelow:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e A.sub.f B.sub.g O.sub.x,

wherein

A=one or more elements selected from groups VB (e.g. V, Nb, Ta), VIB(e.g. Cr, Mo, W), VIIB (e.g. Mn, Tc, Re) or VIII (e.g. Fe, Co, Ni) ofthe periodic table;

B=at least one alkali promoter selected from groups IA (e.g., Li, Na, K)or IIA (e.g., Mg, Ca) of the periodic table;

a=0.01 to 12;

b=0.01 to 12;

c=0.01 to 2;

d=0.01 to 10;

e=0.01 to 1;

f=0 to 2, preferably from 0.01 to 1;

g=0 to 1, preferably from 0.001 to 0.5; and

x=the number of oxygen atoms required to satisfy the valencyrequirements of the elements present.

The numerical values of a, b, C, d, e, f, g, and x represent therelative gram-atom ratios of the elements, respectively, in thecatalyst, where x is a number required to satisfy the valencerequirements of the other elements. The elements are present incombination with oxygen, preferably in the form of various oxides.

The invention also relates to an improved selective low temperaturecatalytic process for the production of nitriles from theircorresponding olefins, particularly for the production of acrylonitrilefrom propylene.

Other objects as well as aspects, features and advantages of the presentinvention will become apparent from a study of the presentspecification, including the claims and specific examples.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a graphical representation of photoelectron spectroscopy (XPS)patterns of a catalyst according to one embodiment of the invention anda comparative catalyst.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the invention relates to an improved ammoxidationcatalytic system for the production of unsaturated nitrites from theircorresponding olefins, in particular, for the production ofacrylonitrile from propylene. More specifically, the present inventionis directed to an improved ammoxidation catalyst containing niobium asan essential element for enhancing activity and selectivity of thecatalyst system. The aim of the present invention is to incorporate anew element into the Bi/Mo system which can improve the catalystperformance. This is achieved by incorporating niobium into abismuth/molybdenum/vanadium/antimony catalyst system.

The improved ammoxidation catalytic system of the invention comprisesthe atomic composition described by the empirical formula set forthbelow:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e A.sub.f B.sub.g O.sub.x,

wherein

A=one or more elements selected from groups VB (e.g. V, Nb, Ta), VIB(e.g. Cr, Mo, W), VIIB (e.g. Mn, Tc, Re) or VIII (e.g. Fe, Co, Ni) ofthe periodic table;

B=at least one alkali promoter selected from groups IA (e.g., Li, Na, K)or IIA (e.g., Mg, Ca) of the periodic table;

a=0.01 to 12;

b=0.01 to 12;

c=0.01 to 2;

d=0.01 to 10;

e=0.01 to 1;

f=0 to 2, preferably from 0.01 to 1;

g=0 to 1, preferably from 0.001 to 0.5; and

x=the number of oxygen atoms required to satisfy the valencyrequirements of the elements present.

The catalysts of the invention can be used with or without a support.Suitable supports for the catalysts include alumina, silica, titania,zirconia, zeolites, silicon carbide, molecular sieves and othermicro/nonporous materials, and mixtures thereof. When used on a support,the supported catalyst usually comprises from about 10 to 50% by weightof the catalyst composition, with the remainder being the supportmaterial.

Another aspect of the invention relates to methods of using the catalystsystem of the invention. More specifically, the invention relates to animproved method of producing unsaturated nitriles from theircorresponding olefins.

One preferred embodiment of the invention relates to an improved processfor the catalytic preparation of acrylonitrile or metha acrylonitrile bythe reaction of propylene or isobutylene with molecular oxygen andammonia at a temperature of between about 200 to 600° C. using theammoxidation catalytic system of the invention.

Preferably, the process achieves a propylene conversion of at least 65%,more preferably at least 70% and most preferred at least 75% using thecatalytic system of the invention.

Preferably, the selectivity in mol % to acrylonitrile is greater than80%, more preferably greater than 85%. The yield of acrylonitrile in mol% is preferably greater than 50%, more preferably greater than 55%, evenmore preferably greater than 60% and most preferred greater than 65%.

EXAMPLES

The following examples are illustrative of some of the catalysts andmethods of making and using the same falling within the scope of thepresent invention. They are, of course, not to be considered in any waylimitative of the invention. Numerous changes and modifications can bemade with respect to the invention.

The basic catalyst of the present invention is a mixed metal oxidecatalyst, which could be prepared according to any procedure well knownby those skilled in the art. Methods used to prepare a catalyst withniobium as an essential element according to one embodiment of theinvention and a comparative catalyst are given below. The catalysts wereprepared by the methods described in U.S. Pat. No. 4,405,498, hereinincorporated by reference.

As used in the following examples, the following terms are defined inthe following manner:

1. "W/F" is defined as the weight of the catalyst in grams divided bythe flow rate of the reactant stream in ml/sec measured at S.T.P.##EQU1##

Example 1 (Comparative Catalyst) Bi Mo V₀.175 Sb₀.35 O_(x) /50% Silica

Part A

10.2 g of Sb₂ O₃ was slurried in 20 ml water along with 3.18 g V₂ O₅.The mixture was boiled until a paste was formed. The paste was thendried at 120° C. and calcined under airflow at 760° C. for 2 hrs.

Part B

97 g Bi(NO₃)₃ 5H₂ O was dissolved in 184 ml water and 30 ml HNO₃(concentrated). Separately, 28.78 g MoO₃ was dissolved in 72 ml waterand 30 ml concentrated NH₄ OH. The two solutions were mixed together andthe pH was adjusted to 4 using NH₄ OH. The mixture was then boiled ca. 2hours, filtered and washed with ca. 1000 ml water.

Part C

The pH of 297 g of a silica solution 30 wt % was adjusted with HNO₃ topH=2 to form Part C. Parts A and B were then added to Part C. Themixture was stirred for several hours, then dried at 120° C. andcalcined under airflow at 550° C. The resultant catalyst wascharacterized by means of an XPS technique. The results are shown inFIG. 1.

Example 2 Bi Mo Nb₀.1 V₀.175 Sb₀.35 O_(x) /50% Silica

This catalyst was prepared according to the above described method setforth in Example 1. Niobium was introduced to the system using therequired amount of niobium pentaoxide added to the molybdenum solutionin Part B. However, any source of niobium could be used for the samepurpose.

The catalyst was characterized by means of an XPS technique. The resultsare shown in FIG. 1.

Catalyst Test

The calcined catalysts of Examples 1 and 2 were crushed to 35-60 meshfraction. 5 g of each catalyst were charged into a tubular fixed bedstainless steel reactor.

The reaction was carried out under 475° C. at atmospheric pressure withthe following feed composition: propylene/O₂ /NH₃ /He=7.9/16.8/10/65.3and a space velocity "W/F" of 3.

Comparison

The catalysts of Example 1 and Example 2 were tested under the similarconditions listed above.

After reaching the steady state, the reactor effluents were analyzedusing a modern gas chromatograph (HP 6890), equipped with both FID andTCD detectors. HCN was collected for a given period of time and thentitrated.

Activity results were calculated according to the equations given above.Results are summarized in the following table.

                                      TABLE I                                     __________________________________________________________________________    Propylene    ACN     ACCN    ACROLEIN                                                                              CO.sub.x                                                                              HCN                                    Conversion                                                                           Y   S   Y   S   Y   S   Y   S   Y   S                            __________________________________________________________________________    Example 1                                                                           62.9   48.7                                                                              77.5                                                                              3.1 4.9 0   0   10.0                                                                              16.0                                                                              0.6 0.9                          Example 2                                                                           77.4   67.9                                                                              87.7                                                                              2.6 3.4 0.9 1.1  5.3                                                                               6.9                                                                              0.3 0.3                          __________________________________________________________________________     ACN: Acrylonitrile                                                            ACCN: Acetonitrile                                                            HCN: Hydrogen cyanide                                                         Y: Yield in mol %                                                             S: Selectivity in mol %                                                  

As shown in the above Table I, the activity of catalyst of Example 2(containing niobium) is higher than the comparative catalyst ofExample 1. The selectivity was significantly enhanced at the cost oftotal oxidation and HCN formation.

The activity and selectivity improvement is believed to be attributed tothe catalyst surface enrichment with bismuth as a result of niobiumintroduction to the system. This is demonstrated in the XPS resultsshown in FIG. 1.

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

What is claimed is:
 1. A process for the production of unsaturatednitriles from the corresponding olefins which comprises reacting theolefins with a gas containing molecular oxygen and ammonia in the vaporphase at a temperature from about 200° C. to 550° C. in the presence ofa catalyst having the empirical formula:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e A.sub.f B.sub.g O.sub.x,

wherein A=one or more elements selected from groups VB, VIB, VIIB orVIII of the periodic table; B=at least one alkali promoter selected fromgroups IA or IIA of the periodic table; a=0.01 to 12; b=0.01 to 12;c=0.01 to 2; d=0.01 to 10; e=0.01 to 1; f=0 to 1; g=0 to 0.5; and x=thenumber of oxygen atoms required to satisfy the valency requirements ofthe elements present.
 2. The process of claim 1, wherein e is from 0.05to 0.5.
 3. The process of claim 1, wherein said olefins are selectedfrom propylene, isobutylene or mixtures thereof and said nitriles areselected from acrylonitrile, methacrylonitrile or mixtures thereof. 4.The process of claim 2, wherein said olefins are selected frompropylene, isobutylene or mixtures thereof and said nitrites areselected from acrylonitrile, methacrylonitrile or mixtures thereof. 5.The process of claim 1, wherein said catalyst is a supported catalystsupported on a catalyst support material selected from silica, alumina,zirconia, titania, alundum, silicon carbide, alumina-silica, inorganicphosphates, silicates, aluminates, borates and carbonates, pumice,montmorillonite, or mixtures thereof.
 6. The process of claim 5, whereinsaid catalyst support material is silica.
 7. The process of claim 5,wherein the supported catalyst comprises 10-50% by weight of thecatalyst, with the remainder being the catalyst support material.
 8. Theprocess of claim 1, wherein said catalyst contains niobium derived froma niobium source soluble in water.
 9. The process of claim 1, whereinsaid process achieves an olefin conversion of at least 65%.
 10. Theprocess of claim 1, wherein said process achieves a selectivity in mol %to nitrites greater than 80%.
 11. The process of claim 1, wherein saidprocess achieves a nitrites yield in molt greater than 50%.
 12. Theprocess of claim 1, wherein said catalyst contains niobium derived fromniobium pentoxide.
 13. The process of claim 1, wherein f ranges from0.01 to 1 and g ranges from 0.001 to 0.5.
 14. The process of claim 1,wherein f ranges from 0.01 to
 1. 15. The process of claim 1, wherein granges from 0.001 to 0.5.
 16. The process of claim 1, wherein saidprocess achieves an olefin conversion of at least 70%.
 17. The processof claim 1, wherein said process achieves an olefin conversion of atleast 75%.
 18. The process of claim 1, wherein said process achieves aselectivity in mol % to nitrites greater than 85%.
 19. The process ofclaim 1, wherein said process achieves a nitrites yield in mol % greaterthan 60%.
 20. The process of claim 1, wherein said process achieves anitrites yield in mol % greater than 65%.
 21. The process of claim 1,wherein said catalyst consists essentially of Bi-Mo-V-Sb-Nb-A-B.